Python 3: don't convert module arguments to bytes

Fixes a test failure:

    ======================================================================
    ERROR: test_module_utils_basic_ansible_module_creation (units.module_utils.test_basic.TestModuleUtilsBasic)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "/home/mg/src/ansible/test/units/module_utils/test_basic.py", line 250, in test_module_utils_basic_ansible_module_creation
        supports_check_mode=True,
      File "/home/mg/src/ansible/lib/ansible/module_utils/basic.py", line 470, in __init__
        self._check_required_arguments()
      File "/home/mg/src/ansible/lib/ansible/module_utils/basic.py", line 1050, in _check_required_arguments
        self.fail_json(msg="missing required arguments: %s" % ",".join(missing))
      File "/home/mg/src/ansible/lib/ansible/module_utils/basic.py", line 1445, in fail_json
        sys.exit(1)
    SystemExit: 1
    -------------------- >> begin captured stdout << ---------------------
    {"msg": "missing required arguments: foo", "failed": true}

because converting 'foo' to bytes yields b'foo' on Python 3, which
doesn't match the native-unicode 'foo' argument spec.

lib/ansible/module_utils/basic.py

@@ -1240,7 +1240,10 @@ class AnsibleModule(object):
 
     def _load_params(self):
         ''' read the input and return a dictionary and the arguments string '''
-        params = json_dict_unicode_to_bytes(json.loads(MODULE_COMPLEX_ARGS))
+        params = json.loads(MODULE_COMPLEX_ARGS)
+        if str is bytes:
+            # Python 2
+            params = json_dict_unicode_to_bytes(params)
         if params is None:
             params = dict()
         return params